Bromodeoxyuridine (BrdU) suppresses the appearance of proteins associated with the differentiated state of various embryonic tissues without significantly affecting cell viability. Low doses of BrdU are proposed to inhibit "switching loci" for differentiation (Weintraub, H. et al. (1973) Nature New Biol. 244:142-143). For instance, BrdU blocks myogenic differentiation and decreases the expression of the MyoD1 regulatory protein (Tapscott, S. J. et al. (1989) Science 245:532-536). Forced expression of MyoD1 from an expression vector in BrdU-treated myoblasts overcomes the differentiation block. BrdU thus appears to selectively block regulatory genes important for cellular development (Tapscott et al., supra).
The immortalized myc embryonic quail cardiomyocyte (MEQC) cell line is induced to differentiate by coculturing with NIH 3T3 cells in a defined synthetic medium (Jaffredo, T. et al. (1991) Exp. Cell Res. 192:481-491). Muscle-specific markers are expressed in cardiac cells as soon as one day after coculture. Treatment with low concentrations of BrdU before coculture prevents phenotypic marker expression, presumably by blocking the expression of genes responsible for differentiation (Niu, S. et al. (1996) Gene 175:187-191).
In an attempt to identify genes involved in avian development, MEQC transcripts attenuated by BrdU treatment were identified by a subtraction hybridization procedure. One corresponding transcript subsequently cloned from an embryonic chick heart cDNA library encodes a putative 215 amino acid protein designated px19 (Niu et al., supra). In five-day chick embryos, px19 mRNA is expressed in hematopoietic cells in liver. In earlier embryos, px19 is strongly expressed in the blood islands of area opaca, which is the location of hematopoiesis in early avian development. Niu et. al. suggest that the px19 protein may therefore be associated with hematopoiesis in early chick development.
The px19 amino acid sequence contains two predicted (.alpha.-helices with oppositely oriented amphipathic surfaces. Each helix contains an LEA (late embryogenesis abundant) consensus sequence, which had previously been described only in plant seed-specific proteins (Puupponen-Pimia, R. et al. (1993) Plant Mol. Biol. 23:423-428). In certain plants, LEA proteins accumulate in embryo tissues as the tissues approach maturity and begin to desiccate. LEA proteins can also be induced by desiccation stress at other plant developmental stages. LEA plant proteins may thus play a role in the protection of plant cells during water loss (Puupponen-Pimia, et al., supra).
The discovery of polynucleotides encoding a human LEA motif protein, and the molecules themselves, provides a means to investigate cellular development and differentiation under normal and disease conditions. Discovery of a human LEA motif protein satisfies a need in the art by providing new compositions useful in diagnosing and treating disorders relating to aberrant cell growth and differentiation including cancer.